The present invention relates to projectiles and in particular to a projectile having a cavity containing a fluid.
To obtain a satisfactory range from a projectile it is necessary to stabilize its orientation to prevent excessive yaw or pitch. While judicious design of the center of gravity or the inclusion of fins may provide an aerodynamic moment which assures stability, a large class of projectiles rely on spin stabilization. Through the use of rifling, a launched projectile is spun about its longitudinal axis so that it exhibits the well-known gyroscopic effect. To ensure that a projectile is gyroscopically stabilized its spin rate must exceed a minimum which is determined by factors such as its mass distribution.
A specific cannon or gun having standard rifling does not have the ability to adjust the spin rate or the stability of various projectiles. In order to vary the spin rate a known barrel employed two interlaced riflings having differing twist rates. A projectile having engravings matching the appropriate one of the riflings is manually inserted therein. This approach however, does not allow continuous adjustment of spin rate and does not affect projectile stabilizing characteristics such as its mass distribution. In a known projectile, a slipping obturator is used to reduce the spin rate. This apparatus is exposed to high stress and does not provide for adjustment of stabilizing factors such as the mass distribution of the projectile. In a known launcher, its barrel is spun at a rate appropriate for the projectile being fired. While the spin rate can be adjusted in this apparatus, the highest rate attainable is limited and wear is a problem.
The present invention provides a projectile whose flight stability is controlled by a fluid disposed in a cavity of the projectile. The cavity is arranged to allow shifting of the fluid. The resulting mass redistribution can affect flight stability by altering the moment of inertia or the center of gravity as the projectile is trajected. Such mass redistribution can be utilized to increase or decrease the flight stability, in various embodiments. Also, prior to launch the flight stability can be set by the simple expedient of selecting a specific volume or density of fluid. The setting of stability in this fashion may be performed in the factory or in the field. This latter feature is also useful where a standard shell is to be fitted with any one of variously shaped explosives of differing densities.
In addition, for some embodiments the fluid employed may be a liquid explosive so that dead weight is avoided.
Moreover this shifting of fluid may be arranged to facilitate high angular acceleration during launch, thereby ensuring rapid attainment of the rated spin rate. In some embodiments the fluid shift may occur over a predetermined interval so that the projectile stability varies throughout its trajectory. This feature may be important where it is desired to destabilize the projectile and cause it to fall when it reaches a target.